EFFECTIVENESS OF FLOATING WAVE ATTENUATORS FOR RESTORING AND PROTECTING COASTAL MARSH OCEAN & COASTAL CONSULTANS, INC. DOUGLAS GAFFNEY, PE RONALD MUNOZ, EIT November 16, 2010 1
OUTLINE Historic Marsh Losses Preliminary Design Considerations Sediment Deposition Fetch Limited Waves Site Location Types Of Floating Wave Attenuators Cost Analysis Preferred Wave Attenuators Requirements for Final Design Questions 2
HISTORIC MARSH LOSS IN JAMAICA BAY (1924 1999) 3
PRELIMINARY DESIGN CONSIDERATIONS SEDIMENT DEPOSITION IS POSSIBLE Select a site where sediment deposition is possible Wave Attenuator: Reduces wave energy transmission by reflection or refraction or both Reduction in wave energy can decrease fluid velocity Decreased fluid velocity allows for deposition of sediment Attenuate waves not current 4
PRELIMINARY DESIGN CONSIDERATIONS FETCH LIMITED WAVES Select a site with fetch limited waves Shorter wavelengths than depth limited waves Allow for smaller height of wave attenuator For effective attenuation 4 wave height of less 4 sec period or less Jamaica Bay wind data JFK airport (1948 2005) Wind speeds greater than 20 mph 5
PRELIMINARY DESIGN CONSIDERATIONS SITE LOCATION Select a site with: Sufficient water depth Facing a dominant wind direction Minimal to no wave reflective effect Good bottom condition Examples: Site 1 and 2 are optimal Site 3 is sub-optimal (strong tidal currents) 6
PRELIMINARY DESIGN CONSIDERATIONS FLOATING WAVE ATTENOR SELECTION Requirements of Wave Attenuator Provide wave attenuation Wave Transmission Coefficient is key parameter Verified with physical or numerical models Varies with wave attenuator, mooring system, module connections, module width, wave climate, depth, etc. Floating Able to be placed in shallow or deep areas Minimal disturbance to benthic environment Anchoring Draft Ease of installation Durability during year-round deployment Cost 7
PRELIMINARY DESIGN CONSIDERATIONS TYPES OF WAVE ATTENORS Box Pontoon Tethered Float Mat Floating Island 8
PRELIMINARY DESIGN CONSIDERATIONS BOX FLOATING WAVE ATTEUATOR Box Most common Typically reinforced concrete modules Either empty (HDPE ballast) or polystyrene filled Flexible connections High internal forces Fixed pile anchoring systems 9
PRELIMINARY DESIGN CONSIDERATIONS TETHERED FLOAT WAVE ATTEUATOR Tethered Float Transportable wave protection system Deep water applications for open ocean Attenuates wave energy via drag produced during rapid and vigorous oscillations of a field of buoyant spheres tethered to remain just below surface High cost Minimal technical data 10
PRELIMINARY DESIGN CONSIDERATIONS MAT FLOATING WAVE ATTEUATOR Mat Easy installation and removal Easy construction Low anchoring loads Less reflection and more refraction Dissipitates more energy Cost effective 11
PRELIMINARY DESIGN CONSIDERATIONS MAT FLOATING WAVE ATTEUATOR Source: http://www.wavebraakker.com/floating-breakwater.htm 12
PRELIMINARY DESIGN CONSIDERATIONS FLOATING ISLAND WAVE ATTEUATOR Floating Island Buoyant mats with planted gardens Made from recycled plastic and foam Ecological benefits Pollution removal Habitat Cost effective Aesthetics Low draft Source: http://www.floatingislandinternational.com/ 13
PREFERED WAVE ATTEUATOR - COST ANALYSIS Type Materials Labor and Total Equipment WaveBraakker $640,000 $150,000 $1,198,000 Timber Log Bundle $100,000 $175,000 $415,000 WaveBreak $765,000 $150,000 $1,388,000 Floating Island $440,000 $165,000 $921,000 Assumptions Each floating wave attenuator is 2,500 linear feet. Floating wave attenuator units will be fully assembled during permitting phase. Marine contractor can install 2,500 linear feet of floating wave attenuator in 3 weeks. Water depth is approximately 10 feet at installation sites. Staging area within 5 nautical miles. Navigation markers will be attached to each floating wave attenuator to address safety. Total price includes 50% markup (5% general conditions, 10% profit, 10% overhead, and 25% contingency). 14
PREFERED WAVE ATTEUATOR - TYPE Timber bundle or Timber Matrix floating wave attenuator Floating Island wave attenuator 15
FINAL DESIGN REQUIREMENTS Investigate sediment transport, wave and hydraulic processes, and foundations Obtain detailed bathymetry data for project site Detailed fetch analysis 16
QUESTIONS & CONTACT INFO? Ocean & Coastal Consultants Douglas Gaffney, PE 20 E. Clementon Rd. Gibbsboro, NJ 08026 DoGa@COWI.Com 856-248-1200 Ronald Munoz, EIT 20 E. Clementon Rd. Gibbsboro, NJ 08026 RoMu@COWI.Com 856-248-1200 17
Supplemental (not part of presentation) 18
ANCHORING SYSTEMS Deadweight Anchor Can be casted concrete or large rock Must be sufficient static friction on bottom to resist movement Pile Anchor Designed for soil's ultimate lateral resistance Embedment Anchor & Screw Anchor Difficult to install in firm marine soil Weak in soft soils Fairly short lengths 19
ANCHORING SYSTEMS Duckbill Helical screws Piles 20
ANCHORING LOAD DETERMINATION 21
WAVE ATTENUATION 22